Characterisation of the microstructure and deformation of high modulus cellulose fibres

This paper reports on the microstructure and deformation of one type of high modulus cellulose fibre characterised using the techniques of Raman spectroscopy and synchrotron X-ray diffraction and it compares this fibre to a lower modulus conventional viscose fibre. The crystallinity of the fibres has been determined using X-ray diffraction. The orientation parameter has been determined by measuring the width of the (200) equatorial reflections for each fibre using microfocus synchrotron radiation and it has also been shown that the crystal orientation parameter varies from the skin to core of the fibres and is different for each type. Mechanical properties of the fibres are reported and it is shown that the high modulus cellulose fibres have very different stress-strain behaviour to the viscose fibres. Finally, it is shown for the high modulus fibre that the 1414, 1260, 1095 and 895 cm⁻¹ Raman bands shift under the application of tensile deformation towards a lower wavenumber with the 1095 cm⁻¹ band giving information about the backbone chain stretching of the cellulose. The viscose fibres show less significant shifts in this peak. The crystal modulus of the high modulus cellulose fibre has also been determined by calculating the change in the c-spacing upon the application of tensile deformation to individual cellulose monofilaments. This change in the c-spacing is determined from the change in position of the (002) meridional reflection giving a crystal modulus of 77 GPa. This value is a little low compared to other published data, and reasons for this are discussed. The shear modulus between crystallites is also calculated and compared to previously published data.     

Crystalline and amorphous deformation of process-controlled cellulose-II fibres

Raman spectroscopy has been used as a tool to monitor the microdeformation of a range of process-controlled fibres with different orientations. The mechanical properties of the fibres are shown to be related to the orientation parameter (〈sin²θ〉), and that by using the particular fibre spinning process (N-methylmorpholine N-oxide (NMMO)/cellulose), a plateau is reached, beyond which no improvements can be made. Clear shifts in the 1095 cm⁻¹ Raman band towards a lower wavenumber are observed upon the application of external tensile deformation, which are thought to relate to the molecular deformation of the cellulose chain. It is found that relationships are determinable between the rate of band shift with respect to strain of the 1095 cm⁻¹ Raman band and the orientation parameter. For the first time, a modified series model is related to the molecular deformation as revealed by Raman spectroscopy, and that the data for these fibres is consistent with a structure with a dominant amorphous fraction. Other high modulus cellulose fibres are shown to behave more like high performance polymer fibres such as poly(p-phenylene benzobisoxazole) (PBO) and poly(p-phenylene terephtalamide) (PPTA). The need, if high performance variants of these fibres are to be developed, to improve the microstructure of NMMO-cellulose fibres is discussed.     

Deformation mechanisms in polymer fibres and nanocomposites

This review covers the development of the understanding of the deformation micromechanics of both synthetic and natural polymeric fibres using spectroscopic and X-ray diffraction techniques. The concept of fibres as composites, where hard and stiff phases are combined with softer polymeric materials is also discussed. Starting with the first discoveries on the molecular orientation and morphology of polymeric fibres, the widely used concepts of uniform stress and strain are examined for the analysis of fibre deformation. The use of advanced techniques such as Raman and infrared spectroscopies to follow molecular deformation in both rigid-rod (e.g. PpPTA, PBO, PBT, polyethylene) and natural (e.g. cellulose, collagen, silk, chitin) polymer fibres is presented. A clear distinction between fibres that have structures that are subjected to uniform stress or strain is presented, with the evidence that is detected from the response of the molecules (by Raman spectroscopy) and the crystalline fraction (by X-ray diffraction). It is suggested that natural fibres, such as cellulose, silk and others, may have different types of microstructures that are subjected to a uniform strain, which could have potentially led to incorrect determinations of crystal moduli. It is also demonstrated that the Raman and X-ray techniques have been influential on our development of fibres, and have shown that the morphology plays a critical role in mechanical properties. In addition to this, the use of X-ray diffraction using microfocus synchrotron sources is also reviewed. This approach allows a more complete picture of both molecular and crystalline deformations to be developed, and with the advent of nanocomposites it is shown that a combination of the two techniques will be vital for our understanding of their exploitation in technological applications.     

Effect of dissolving conditions on the structure and physicomechanical properties of hydrocellulose fibres spun from solutions of cellulose in N-methylmorpholine-N-oxide

Conclusions Hydrocellulose fibres have been prepared from solutions of cellulose in N-methylmorpholine-N-oxide which have been prepared by two different methods (traditional and accelerated).It has been shown that the properties of the fibres obtained depend on the method of preparing the spinning solution.The fibres which have been spun from solutions prepared by the accelerated method have elevated deformation characteristics; this is connected with their specific supermolecular structure.Translated from Khimicheskie Volokna, No. 2, pp. 17–19, March–April, 1990.     

Preparation of hydrocellulose fibres with increased elasticity from solutions of cellulose in n-methylmorpholine-n-oxide

Conclusions The deformation properties of hydrocellulose fibres spun from solutions of cellulose in N-methylmorpholine-N-oxide monohydrate are determined to a considerable degree by the character of structure formation in the precipitation stage.A considerable improvement in the deformation properties of hydrocellulose fibres has been achieved due to the realization of a process of crystallization of the MMO at a definite stage in spinning; this affects the formation of a supermolecular structure in the polymer system.Translated from Khimicheskie Volokna, No. 4, pp. 33–35, July–August, 1989.     

Lyocell fibres based on direct dissolution of cellulose in N-methylmorpholine N-oxide: Development and prospects

The scientific principles of direct dissolution of cellulose in the NMMO—water system demonstrate the major possibility of obtaining concentrated spinning solutions and spinning hydrated cellulose fibres from them. The specific features of the properties of NMMO (high boiling point and insufficient thermal stability) that dissolves the NMMO—water system (narrow concentration range, optimum for dissolution of cellulose) makes it necessary to recycle the washing water by evaporating it, which causes high power consumption for this process. It is expedient to examine the possibilities of membrane technologies, including electrodialysis, for solving problems of recycling the solvent and cutting power consumption. However, this path only allows partially concentrating used washing water, since there is the danger of crystallization of NMMO di-and monohydrate. Spinning through an air gap from highly viscous solutions with long relaxation times at high spinneret draw ratios results in highly oriented fibres with high tensile rigidity (high deformation modulus). Fabrication of fibres whose properties correspond to ordinary viscose fibres will perhaps require “going away” from highly viscous solutions to a lower concentration and spinning by the ordinary wet method, but the volume of solvent used increases significantly, recycling it is more difficult, and power consumption increases. For the same reason of high orientation, the fibres exhibit important fibrillation when wet, and a “peach skin” effect is formed in the finished textiles. To reduce fibrillation, special treatments of the fabrics must be used, biofinishing, for example. During use of the articles, fibrillation can reappear, in laundering, for example. The technology for fabricating fibres of the Lyocell type requires solving many problems. Developing research on selecting alternative solvents and dissolving systems for direct dissolution of cellulose to obtain concentrated spinning solutions is simultaneously useful. __________ Translated from Khimicheskie Volokna, No. 2, pp. 58–64, March–April, 2007.     

An indirect method which ranks the adhesion in natural rubber filled with different types of cellulose fibres by plots of E(t)/Et=0 versus log t

The suggestion that composites with good bonding between fibres and matrix have a faster stress relaxation rate than composites with poor bonding between fibres and matrix is supported here by measurements on natural rubber filled with untreated cellulose fibres, allyl acrylate grafted cellulose fibres and allyl methacrylate grafted cellulose fibres.     

Cellulose fibres, nanofibrils and microfibrils: The morphological sequence of MFC components from a plant physiology and fibre technology point of view

During the last decade, major efforts have been made to develop adequate and commercially viable processes for disintegrating cellulose fibres into their structural components. Homogenisation of cellulose fibres has been one of the principal applied procedures. Homogenisation has produced materials which may be inhomogeneous, containing fibres, fibres fragments, fibrillar fines and nanofibrils. The material has been denominated microfibrillated cellulose (MFC). In addition, terms relating to the nano-scale have been given to the MFC material. Several modern and high-tech nano-applications have been envisaged for MFC. However, is MFC a nano-structure? It is concluded that MFC materials may be composed of (1) nanofibrils, (2) fibrillar fines, (3) fibre fragments and (4) fibres. This implies that MFC is not necessarily synonymous with nanofibrils, microfibrils or any other cellulose nano-structure. However, properly produced MFC materials contain nano-structures as a main component, i.e. nanofibrils.     

Structure of Naturally Coloured Cottons

Abstract

Previous work on the morphology of naturally coloured green suggested than that the secondary wall of the fibres consists of alternate layers of cellulose and a waxy organic substance called suberin. The work described in this paper has shown that modern varieties of green cotton do contain a large proportion of suberin. Data front fibre swelling is consistent with alternate layers of suberin and cellulose in the secondary wall. The naturally coloured fibres have a lower tenacity and work of rupture than conventional white fibres although they have an acceptable level of textile properties. The crystallinity of the coloured fibres is lower than for white cotton, but the cellulose has the cellulose I structure, normally found in cotton.     

Restricted dissolution and derivatization capacities of cellulose fibres under uniaxial elongational stress

Cellulose is a future major source of materials and biofuel but its extraction and its chemical or enzymatic treatments are difficult, polluting and inefficient tasks. The accessibility of the reagents to cellulose chains is indeed limited. Classical evocated reasons for this lack of accessibility are pore structure, tight hydrogen bond arrays, crystallinity and presence of resistant materials like lignin. Studying dissolution of cotton hairs and regenerated cellulose fibres in various solvents under uniaxial tension, we found that tension is preventing these fibres to dissolve in chemicals that would dissolve the same cellulose fibres tension-free. We show that what is controlling dissolution is not the degree of swelling since, at the same degree of swelling, fibres under tension do not dissolve while fibres without tension do. An important result is that when a fibre under tension (thus swollen but not dissolved) is breaking, it is immediately dissolving. Under tension, when the solvent is present around cellulose chains, it is activated to solvate the chains only when tension stress is released. A chemical reaction like acetylation of cellulose fibre under tension also gives an interesting result. The degree of substitution remains very low while the same experiment performed without tension leads to higher degree of substitution followed by the dissolution of the fibre (even increasing further the DS due to homogeneous reaction). We postulate that the lack of dissolution capacity or reacting activity under tension can be due to the hampering of local conformational movements, cellulose chains being not able to perform axial movements. The availability of performing local conformational movements could be a main component of cellulose activation.     

Effects of plasma treatment on mechanical properties of rubber/cellulose fibre composites

Natural rubber materials reinforced with cellulose fibres have been studied with respect to crosslink density, tensile strength and stress relaxation. The fibres have been grafted with butadiene or divinylbenzene by plasma treatment. Chemiluminescence analysis was used to indicate the grafting on the surface of the cellulose fibres and also to estimate the effect of the plasma on the cellulose fibres. The results indicate the possibility of obtaining a surface layer on the fibres, which is a conceivable way of improving the mechanical properties of rubber composites.     

Analysis of the evolution of production of hydrated cellulose textile fibres

In summing up the observations given below on the future of new cellulose fibres, including comparing them with natural fibres (cotton), some generalizations can be made: The constant increase in the demand for cellulose-based textile fibres is not only due to the tendency toward a higher standard for clothing and satisfaction of the needs of the growing population, but also to the specific features of the properties of cellulose fibres (natural and man-made), especially hygroscopicity and hygiene: in this respect, the new fibres for linen clothing are significantly better than synthetic fibres, second to the latter only in fabrics for water-repelllent clothing; an analysis of the possibilities of solving the problem of the increasing demand for cellulose fibres by expanding production of cotton and increasing production of man-made cellulose fibres leads to the following conclusions: the increase in areas planted with cotton could be slowed by an increase in the demand for fields for grains and the limited possibilities of restoring previous catastrophically destroyed sources of irrigation water; while preserving or expanding production of cotton, primarily by increasing productivity, it is necessary to significantly increase production of man-made fibres; for this reason, the main restriction which had previously not permitted adding new HC fibre enterprises primarily produced by the viscose process, which does not meet current ecological requirements, has been removed; for this reason, the advances in spinning of cellulose fibres from solutions in direct solvents (primarily MMO) make this method fundamental in solving the problem of satisfying the demand for cellulose fibres; in using the new method of manufacturing HC fibres, one of the serious conditions for increasing total production of chemical fibres should also be considered; this does not eliminate the need for progress in the synthetic fibre field, although with respect to some physical, particularly strength, properties, MMO fibres can partially take on the function of textile materials which synthetic, basically polyester, fibres currently fulfill; some properties of the new fibres, in particular, their capacity for surface fibrilation, require improvement, but although this is difficult, it is nevertheless a totally solvable problem. The questions discussed in the present article require further elaboration and more precise definition, but they undoubtedly constitute an important part of the overall prognosis for production and correspondingly scientific studies of fibres.Translated from Khimicheskie Volokna, No. 3, pp 17–19, May–June. 1996.     

X-ray diffraction method of determining the degree of crystallinity of cellulose materials of different anisotropy

It is shown that the important change in the x-ray diffraction parameters in preparation of compact products from microcrystalline cellulose and ground cotton fibres by pressing is not due to the amorphous phase of cellulose. A method for determining the degree of crystallinity of cellulose in anisotropic materials using an external standard that ensures spherical scattering symmetry is substantiated. The applicability of the proposed approach for estimating the degree of crystallinity of cellulose fibres directly in fabrics, which reduces the duration of the experimental procedures by 3–4 times, is demonstrated.Translated from Khimicheskie Volokna, No. 6, pp. 28–32, November–December, 2004.     

世界纤维素纤维用染料现状和发展趋势

纤维素纤维是一类重要的纺织纤维 ,用于其印染的染料状况反映了整个染料工业的技术水平。本文阐述了世界纤维用染料的现状 ,并指出了近年的发展状况。     

Mechanical properties of natural rubber/grafted cellulose fibre composites

Mechanical properties of natural rubber/allyl acrylate and allyl methacrylate grafted cellulose fibre composites are presented. Stress/strain measurements and dynamic mechanical measurements indicate that the adhesion between grafted fibres and matrix is better than that in samples containing untreated cellulose fibres. This makes it possible to vary the composite properties by varying the fibre type and/or fibre amount.     

Influence of chemical treatments on the electrokinetic properties of cellulose fibres

Changes in the surface composition of chemically treated cellulose fibres obtained from the sheath of banana plants were investigated using electrokinetic (ζ-potential) measurements. Scanning electron microscopy (SEM) was used to observe changes in the surface morphology of the fibres. Spectroscopic methods were also used to analyse the changes on the cellulose fibre surface. Chemical treatments such as alkali treatment, acetylation, treatment with a triazine coupling agent, various silanes, etc. reduced the hydrophilicity of the fibres. The surface morphology of the fibres showed considerable changes. Chemical treatments reduced the acidity of the already polar cellulose fibre. The high iso-electric point (IEP) of the silane A1100-treated fibres shows that basic groups dominate at these surfaces. The observations are consistent with the values obtained using solvatochromic measurements.     

Effect of preliminary loading on the deformation and strength properties of high-strength fibres

High-strength, high-modulus polyethylene fibres fabricated with gel technology is similar to low-modulus fibres of the olefin and amide series (Capron, polypropylene) with respect to the character of the correlation of the stress—strain diagrams and curve of accumulation of the residual component of deformation. The residual deformation component is relatively large both for high-strength PE fibre and for p-polyamide fibres. The differences in the character of accumulation of the plastic component in these fibres are due to the fact that the residual strains arising in high-strength PE fibre, as in other flexible-chain polymer fibres (polypropylene, Capron) is initiated by breaking of bonds in the main chain. In p-polyamide fibres (Armos, SVM, Terlon, Kevlar), plastic strains arise due to highly elastic deformation “frozen≓ by hydrogen bonds and orientation of molecular chains. Preliminary deformation affects the strength properties of high-modulus fibres differently: in PE fibres, the strength decreases, it increases for Armos and SVM fibres, and remains unchanged for Terlon fibre. This difference is to a great degree due to the difference in the types of intermolecular interaction in fibres of the olefin and amide series. For all fibres investigated, the character of accumulation of the residual deformation component can be correlated with the type of stress—strain diagram, which will allow creating simpler methods of evaluating residual strains. Translated from Khimicheskie Volokna, No. 3, pp. 30–33, May–June, 1998.     

Role of precipitation bath components in the manufacture of viscose fibres

Conclusions An analysis has been made of data on structure formation processes in spinning viscose fibres and of the connection of the primary structure with the properties of the finished fibres and yarns.It has been shown that the attainment of high physicomechanical and operational properties of viscose fibres is possible by preventing premature crystallization of the cellulose in the freshly-spun gel-fibre.Retardation of the cellulose crystallization process in spinning viscose fibres is advisably effected as a result of reducing the activity of water in the precipitation bath.Translated from Khimicheskie Volokna, No. 1, pp. 8–13, January–February, 1986.     

Polyolefins–biofibre composites: A new way for an industrial production

Low density polyethylene (LDPE) composites based on cellulose fibres have been processed by high shear extrusion with water injection to help dispersion of fibres and release nanofibres from cellulose. Influence of extrusion parameters as shear, residence time, storage conditions of the matrix, and effect of water injection on the morphological properties of the composites have been studied using microscopy. Optimization of the extrusion parameters is necessary to reach a dispersion of the fibres. Increasing shearing forces and residence time allows limiting the presence of large aggregates of cellulose fibres. Use of powdered LDPE, even for short residence time and low shear, is efficient to produce well‐dispersed composites. Injection of water during the extrusion also improves the quality of the dispersion. However, no nanofibres are observed. The main effect is a spectacular decrease of the discoloration (yellowing) due to cellulose degradation. Mechanical properties of the composites have been investigated. Young modulus increases with cellulose content and reinforcing effect is more important above 10% by weight. For well‐dispersed composites, the extrusion parameters have no significant influence on the stiffness of the composites. However, due to the weakness of the interface, the ductility of composites is reduced compared with LDPE. POLYM. ENG. SCI., 47:467–476, 2007. © 2007 Society of Plastics Engineers.     

Raman spectroscopy of Kevlar fibres during deformation—Caveat emptor

It has been demonstrated that when aromatic polyamide fibres such as Kevlar 49 are subjected to mechanical deformation, significant frequency shifts are obtained for the peak position of the 1610 cm^?1 Raman band using both 632·8 nm and 488 nm laser radiation. Two earlier reports of the deformation of fibres in a 488 nm argon ion laser beam reported no such frequency shifts. It has been shown that this wavelength of laser light can degrade Kevlar fibres. This causes premature failure of the fibres through chain scission and the fibres break at low strains before significant levels of stress or strain can be achieved. Hence, the previous conflicts can be resolved and it has been demonstrated that simultaneous Raman spectroscopy and mechanical deformation is a powerful method of following the micromechanics of fibre deformation.